MK. MANAGEMENT
AGROEKOSISTEM
HUBUNGAN AIR-TANAH-TANAMAN
Disarikan oleh:
Prof Soemarno ( Sept 2013)
Soil Water Relationships
CIRI-CIRI TANAH
• Tekstur Tanah
– Definition: relative proportions of various sizes of
individual soil particles
– USDA classifications
• Sand: 0.05 – 2.0 mm
• Silt: 0.002 - 0.05 mm
• Clay: <0.002 mm
– Textural triangle: USDA Textural Classes
– Coarse vs. Fine, Light vs. Heavy
– Affects water movement and storage
• Struktur Tanah
– Definition: how soil particles are grouped or
arranged
– Affects root penetration and water intake and
movement
SEGITIGA
USDA Textural
TEKSTUR
Triangle
TANAH
• Bulk Density (b)
Ms
b 
Vb
– b = soil bulk density, g/cm3
– Ms = mass of dry soil, g
– Vb = volume of soil sample, cm3
• Typical values: 1.1 - 1.6 g/cm3
• Particle Density (p)
Ms
p 
Vs
– P = soil particle density, g/cm3
– Ms = mass of dry soil, g
– Vs = volume of solids, cm3
• Typical values: 2.6 - 2.7 g/cm3
• Porosity ()
volume of pores
 
volume of soil

b 
  1  100%
p 

• Typical values: 30 - 60%
AIR DALAM TANAH
• Kadar Air Tanah
Mw
m 
Ms
– Mass water content (m)
– m = mass water content (fraction)
– Mw = mass of water evaporated, g
(24 hours @ 105oC)
– Ms = mass of dry soil, g
• Kadar air volumetrik (v)
Vw
v 
Vb
V = volumetric water content (fraction)
Vw = volume of water
Vb = volume of soil sample
At saturation, V = 
V = As m
As = apparent soil specific gravity = b/w
(w = density of water = 1 g/cm3)
– As = b numerically when units of g/cm3 are used
–
–
–
–
–
–
• Equivalent depth of water (d)
– d = volume of water per unit land area = (v A L) / A = v L
– d = equivalent depth of water in a soil layer
– L = depth (thickness) of the soil layer
Volumetric Water Content & Equivalent Depth
(cm3)
Equivalent Depth
(g)
(g)
(cm3)
Volumetric Water Content & Equivalent
Depth
Typical Values for Agricultural Soils
Soil Solids (Particles): 50%
0.50 in.
1 in.
Very Large Pores:
(Gravitational Water)
Total Pore
Space: 50%
15%
0.15 in.
Medium-sized Pores: 20%
(Plant Available Water)
0.20 in.
Very Small Pores:
(Unavailable Water)
0.15 in.
15%
Daya Simpan Air =
Water-Holding Capacity of Soil
Effect of Soil Texture
Coarse Sand
Silty Clay Loam
Dry Soil
Gravitational Water
Water Holding Capacity
Available Water
Unavailable Water
POTENSIAL AIR TANAH
• DESKRIPSI
– Measure of the energy status of the soil water
– Important because it reflects how hard plants must
work to extract water
– Units of measure are normally bars or
atmospheres
– Soil water potentials are negative pressures
(tension or suction)
– Water flows from a higher (less negative) potential
to a lower (more negative) potential
PotenSial AIR TANAH
• Komponen
t
  g  m  o
– t = total soil water potential
– g = gravitational potential (force of gravity
pulling on the water)
– m = matric potential (force placed on the water
by the soil matrix – soil water “tension”)
– o = osmotic potential (due to the difference in
salt concentration across a semi-permeable
membrane, such as a plant root)
– Matric potential, m, normally has the greatest
effect on release of water from soil to plants
• Kurva pelepasan air tanah
– Curve of matric potential (tension) vs. water content
– Less water  more tension
– At a given tension, finer-textured soils retain more
water (larger number of small pores)
Potential Matriks dan Tekstur Tanah
The tension or suction created by small capillary tubes
(small soil pores) is greater that that created by large
tubes (large soil pores). At any given matric potential
coarse soils hold less water than fine-textured soils.
Height of capillary
rise inversely related
to tube diameter
•Kapasitas Lapang= Field Capacity (FC or fc)
–Soil water content where gravity drainage becomes
negligible
–Soil is not saturated but still a very wet condition
–Traditionally defined as the water content
corresponding to a soil water potential of -1/10 to -1/3
bar
•Titik Layu Permanen: Permanent Wilting Point (WP or
wp)
–Soil water content beyond which plants cannot
recover from water stress (dead)
–Still some water in the soil but not enough to be of
use to plants
–Traditionally defined as the water content
corresponding to -15 bars of SWP
AIR TERSEDIA
• Definition
– Water held in the soil between field capacity and
permanent wilting point
– “Available” for plant use
• Kapasitas Air Tersedia: Available Water
Capacity (AWC)
– AWC = fc - wp
– Units: depth of available water per unit depth of
soil, “unitless” (in/in, or mm/mm)
– Measured using field or laboratory methods
(described in text)
Sifat Hidraulik Tanah & Tekstur Tanah
• Fraction available water depleted (fd)
 fc  v 
fd  

 fc  wp 
– (fc - v) = soil water deficit (SWD)
– v = current soil volumetric water content
• Fraction available water remaining (fr)
 v  wp 
fr  

 fc  wp 
– (v - wp) = soil water balance (SWB)
• Total Air Tersedia: Total Available Water (TAW)
TAW = (AWC) (Rd)
– TAW = total available water capacity within the plant
root zone, (inches)
– AWC = available water capacity of the soil,
(inches of H2O/inch of soil)
– Rd = depth of the plant root zone, (inches)
– If different soil layers have different AWC’s, need to sum up
the layer-by-layer TAW’s
TAW = (AWC1) (L1) + (AWC2) (L2) + . . . (AWCN) (LN)
- L = thickness of soil layer, (inches)
- 1, 2, N: subscripts represent each successive soil layer
[Error on page 26 of text: change SWD  TAW ]
Gravity vs. Capillarity
Vertical movement
due largely to gravity
Horizontal movement
due to capillarity
Infiltrasi Air
Def’n.: the entry of water into the soil
Influencing Factors
• Soil texture
• Initial soil water content
• Surface sealing (structure, etc.)
• Soil cracking
• Tillage practices
• Method of application (e.g., Basin vs. Furrow)
• Water temperature
Infiltrasi Kumulatif vs. Tekstur Tanah
Infiltration Rate vs. Time
For Different Soil Textures
Water Infiltration Rates and Soil Texture
Soil Infiltration Rate vs. Constant
Irrigation Application Rate
Soil Infiltration Rate vs. Variable
Irrigation Application Rate
KEDALAMAN PENETRASI
• Can be viewed as sequentially filling the
soil profile in layers
• Deep percolation: water penetrating
deeper than the bottom of the root zone
• Leaching: transport of chemicals from the
root zone due to deep percolation
Water Storage in Layered Soil Profiles
Pengukura Air Tanah
• Gravimetric
–
–
–
–
Measures mass water content (m)
Take field samples  weigh  oven dry  weigh
Advantages: accurate; Multiple locations
Disadvantages: labor; Time delay
• Feel and appearance
– Take field samples and feel them by hand
– Advantages: low cost; Multiple locations
– Disadvantages: experience required; Not highly
accurate
Pengukuran Air Tanah
• Neutron scattering (attenuation)
– Measures volumetric water content (v)
– Attenuation of high-energy neutrons by hydrogen nucleus
– Advantages:
• samples a relatively large soil sphere
• repeatedly sample same site and several depths
• accurate
– Disadvantages:
• high cost instrument
• radioactive licensing and safety
• not reliable for shallow measurements near the soil surface
• Dielectric constant
–
–
–
–
A soil’s dielectric constant is dependent on soil moisture
Time domain reflectometry (TDR)
Frequency domain reflectometry (FDR)
Primarily used for research purposes at this time
Pengukuran Aur Tanah:
Neutron Attenuation
Pengukuran Air Tanah
• Tensiometers
– Measure soil water potential (tension)
– Practical operating range is about 0 to 0.75
bar of tension (this can be a limitation on
medium- and fine-textured soils)
• Electrical resistance blocks
– Measure soil water potential (tension)
– Tend to work better at higher tensions
(lower water contents)
• Thermal dissipation blocks
– Measure soil water potential (tension)
– Require individual calibration
Tensiometer for Measuring Soil Water Potential
Water Reservoir
Variable Tube Length (12 in- 48 in)
Based on Root Zone Depth
Porous Ceramic Tip
Vacuum Gauge (0-100 centibar)
Electrical Resistance Blocks & Meters
. Evaluation of silvicultural treatment effects on infiltration, runoff, sediment yield,
and soil moisture in a mixed conifer New Mexico forest
A. Madrid, A.G. Fernald, T.T. Baker, and D.M. VanLeeuwen
Journal of Soil and Water Conservation May/June 2006 vol. 61 no. 3 159-168
Clearing ponderosa pine forests often increases post-harvest runoff and sediment
yield, yet there is little research to show if partial thinning of mixed conifer forests
similarly produces more runoff and sediment. Rainfall simulations were used to
evaluate silvicultural treatment effects on infiltration, runoff, sediment yield, and
soil moisture in a southern New Mexico mixed conifer forest. Silvicultural
treatments included: untreated control; precommercial thin with slash piled; and
precommercial thin with slash scattered. There were no significant differences in
infiltration rates, runoff rates, or soil moisture. Time to peak runoff was greater on
pile and scatter treatments than on the control during both dry and wet runs.
Sediment yield was greater on pile and scatter treatments than on the control
during wet runs, yet was very low in all cases. We conclude that southwestern
mixed conifer forests may be partially thinned without risk of significant increases
in hillslope runoff and sediment yield.
Infiltration, water repellency, and soil moisture content after broadcast burning a
forest site in southwest Oregon
D.H. McNabb, F. Gaweda, and H.A. Froehlich
Journal of Soil and Water Conservation January/February 1989 vol. 44 no. 1 87-90
Broadcast burning a harvested site in the Mixed-Evergreen Forest Zone of
southwest Oregon in June increased the water repellency and decreased the
infiltration rate of the surface soil for about 5 months. Both the infiltration rate and
the water repellency returned to nearly preburn levels by late November.
Measuring water repellency by the apparent contact angle produced closer
correlation with changes in infiltration capacity than using the water-droppenetration-time test in the field. During the first summer, the moisture content of
soil in the burned plots remained higher than in the unburned plots.
Management effects of crops and crop strip widths on crop yield and
conservation of soil and moisture on a limited-resource farm
U. R. Bishnoi, H. B. Ide, and D. A. Mays
Journal of Soil and Water Conservation March/April 1991 vol. 46 no. 2 147-150
Terracing and other conventional methods of soil and water conservation are often too
expensive for limited-resource farmers to implement. Therefore, research to determine the
effects of three strip widths and three vegetable crops on runoff, soil loss, soil moisture, plant
canopy, and crop yield was conducted on a small farm. The experimental site was located on
a well-drained Baxter cherty silt loam soil (Typic Paleudult) with a 6% slope and a pH of 6.5.
Three crops, sweet corn (Lea mays rugose L.), cv. Silver Queen; snap beans (Phaseolus
vulgaris h.), cv. Contender; and cucumbers (Cucumis sativus L.), cv. Explorer, were planted
at three different strip widths (1.8, 5.5, and 7.3 m) in a split-plot design with four replications,
where strip widths were the main plots and crops were randomized as subplots. Runoff from
the 7.3-m plot width was 60% and 13% less than that from the 1.8-m and 5.5-m plot widths,
respectively. Significantly less runoff was obtained from cucumbers than from other crops.
Cucumbers allowed less soil loss (1.7 Mg ha−1) than sweet corn (1.8 Mg ha−1) and snap
beans (2.1 Mg ha−1). Among the three crops, the most soil water was observed with
cucumber. Significantly denser canopy cover and greater moisture was obtained with the
7.3-m strip width for all crops. Cucumber canopy was 11% and 38% greater than that for
sweet corn and snap beans, respectively. Sweet corn planted in narrow strips produced a
significantly higher yield (37,500 ears ha−1) than sweet corn planted in wide strips (33,600
ears ha−1). The highest yield of snap beans (5,890 kg ha−1) was observed with a 5.5-m strip
width, whereas cucumbers produced most (48,710 kg ha−1) in the 7.3-m wide strip.
Influence of conservation tillage on soil properties
R. L. Blevins, M. S. Smith, G. W. Thomas, and W. W. Frye
Journal of Soil and Water Conservation May/June 1983 vol. 38 no. 3 301-305
Conservation of soil moisture is one of the major advantages of no-till crop production systems.
In a long-term tillage study, higher soil moisture under no-till corn production was observed as
compared with that under conventional tillage throughout the growing season. Significantly less
evaporation occurred under no-till early in the growing season. This conservation of soil water
may carry the no-till crop through short drought periods without severe moisture stresses
developing in the plants. However, the extra water conserved under no-till can occasionally be
detrimental under conditions in which excessive soil water contributes to denitrification losses.
Soil compaction in no-tillage soils was not found to be a problem. Saturated hydraulic
conductivity measurements suggest better water movement in no-tillage compared with
conventional tillage. After 10 years of continuous no-till corn production, no deterioration of soil
physical properties was observed. The most obvious chemical change was the rapid
acidification of the soil surface when high nitrogen fertilizer rates were used. Associated with
reduced soil pH were increased levels of exchangeable aluminum and manganeses.
Exchangeahle calcium was sgnificantly lower for no-till at all soil depths and all nitrogen fertilizer
rates compared with conventional tillage. Potassium was concentrated in the 0-to-5-centimeter
soil layer under no-till and decreased with depth. Exchangeable magnesium in the 0-to-5centimeter soil depth declined with increased nitrogen fertilizer and was lower in no-till than in
conventional tillage. Organic matter was twice as high in the 0-to-5-centimeter soil depth
compared with conventional tillage systems. This modified soil environment affects chemical
reactions and the distribution and activity of microbes. It also has a significant effect on the fate
of surface-applied nitrogen fertilizer. Methods and time of nitrogen fertilizer application may need
some modification to reduce possible nitrogen losses by denitrification or temporary
immobilization of nitrogen.
Soil organic matter and available water capacity
Berman D. Hudson
Journal of Soil and Water Conservation March/April 1994 vol. 49 no. 2 189-194
For the last 50 years, the consensus view among researchers has been that
organic matter (OM) has little or no effect on the available water capacity (AWC) of
soil. The historical development of this viewpoint is traced. It is argued that the the
literature on this subject has been misconstrued and that the consensus view is
wrong. In addition to a critical review of the literature, published data were
evaluated to assess the effect of OM content on the AWC of surface soil within
three textural groups. Within each group, as OM content increased, the volume of
water held at field capacity increased at a much greater rate (average slope = 3.6)
than that held at the permanent wilting point (average slope = 0.72). As a result,
highly significant positive correlations were found between OM content and AWC
for sand (r2 = 0.79***), silt loam (r2 = 0.58***) and silty clay loam (r2 = 0.7G***)
texture groups. In all texture groups, as OM content increased from 0.5 to 3%,
AWC of the soil more than doubled. Soil OM is an important determinant of AWC
because, on a volume basis, it is a significant soil component. In this study, one to
6% OM by weight was equivalent to approximately 5 to 25% by volume.
Responses of Irrigation Water Use and Productivity of Sweet Cherry to SingleLateral Drip Irrigation and Ground Covers
Yin, Xinhua; Seavert, Clark F.; le Roux, Jac
Soil Science. 176(1):39-47, January 2011.
A field experiment was conducted to evaluate the transitional impacts of single-lateral drip
irrigation versus microsprinkler irrigation and wheat straw mulch, black polypropylene cover,
and white polypropylene cover versus no ground cover (but herbicides were used to control
weeds) on irrigation water use and productivity of sweet cherry (Prunus avium L.) trees
(Lapins on Mazzard rootstock) on a fine loam soil at The Dalles, OR, from 2005 through
2007 in a split-plot design with four replicates. Our results showed that during the entire
irrigation season from May to October, drip irrigation consumed only 21% to 29% of irrigation
water relative to microsprinkler irrigation, the current irrigation system, averaged over the
four ground cover systems in the 3 years. Water use efficiency was enhanced by 167% to
234% with drip irrigation over microsprinkler irrigation. Fruit yield and fruit quality including
firmness, color, and size did not differ regardless of irrigation or ground cover system. Drip
irrigation increased marketable fruit by 7% to 12% via reducing fruit surface pitting and
bruising compared with microsprinkler. Straw mulch, black polypropylene cover, and white
polypropylene cover also increased the percentage of marketable fruit in 1 out of 3 years.
Overall, shifting from microsprinkler irrigation to single-lateral drip irrigation does not result in
significant negative impacts on fruit yield or quality of bearing sweet cherry trees. Singlelateral drip irrigation has the potential to be a viable alternate irrigation system for sweet
cherry production, where severe shortage of irrigation water occurs.
Effects of soil moisture, temperature, and nitrogen fertilization on soil respiration and
nitrous oxide emission during maize growth period in northeast China
Changchun Songa* & Jinbo Zhangb
pages 97-106
Acta Agriculturae Scandinavica, Section B - Soil & Plant Science
Volume 59, Issue 2, 2009
To evaluate the response of soil respiration and nitrous oxide (N2O) emission to soil moisture, temperature
and nitrogen fertilization, and to estimate the contribution of soil and rhizosphere to total soil carbon
dioxide (CO2) and N2O emissions, a field experiment was conducted in the Sanjiang Mire Wetland
Experimental Station, Chinese Academy of Sciences, in the northeast of China. The experiment included
four treatments: bare soil fertilized with 150 kg N ha−1 yr−1 (CK), and maize-cropped soils amended with 0
(N0), 150 (N150), and 250 (N250) kg N ha−1 yr−1. The cumulative soil CO2 emission in the CK, N0, N150,
and N250 treatments was estimated to be 698, 863, 962, and 854 g CO 2 C m−2, respectively. The
seasonal soil CO2 fluxes were significantly affected by soil temperature, with a Q 10 value between 1.99
and 2.47. Analysis of the stepwise regression indicated that the CO2 flux can be quantitatively described
by a linear combination of soil moisture content and soil temperature 5 cm below ground. Approximately
70, 58, 60, and 44% of the variability in CO2 flux can be explained by these two parameters, in CK, N0,
N150, and N250, respectively. Nitrogen fertilization with 150 kg N ha−1 yr−1 increased CO2 fluxes by 14.5%
compared with soils fertilized with 0 kg N ha−1 yr−1. However, in the soil fertilized with 250 kg N ha−1 yr−1,
high N fertilization suppressed soil respiration. There was an exponential relationship between soil
temperature 5 cm below ground and N2O flux, with a Q 10 value of 1.30–2.91. Mean cumulative soil N2O
emissions during the maize-growing season in the CK, N0, N150, and N250 treatments were estimated to
be 86, 44, 200, and 484 mg N2O-N m−2, respectively. In contrast to the maize planting, soil fertilized with
150 kg N ha−1 yr−1 and with 250 kg N ha−1 yr−1 increased N2O fluxes by 354 and 1000%, compared with
soils fertilized with 0 kg N ha−1 yr−1, respectively. Soil respiration and N2O fluxes measurement using the
root-exclusion technique indicated that the rhizosphere of the maize could be the dominant habitat of soil
respiration and N2O formation.
Scaling Effect of the Hydraulic Conductivity in a Confined Aquifer
Fallico, Carmine; Vita, Maria Chiara; De Bartolo, Samuele; Straface, Salvatore
Soil Science. 177(6):385-391, June 2012.
Previous studies showed that the values of the representative parameters of an
aquifer, such as the hydraulic conductivity (k), increase with the scale, that is, with
the aquifer volume involved in the measurement. The main cause of this behavior
is commonly ascribed to the heterogeneity of the porous media. Heterogeneity
influences the scaling behavior differently for laboratory or field measurement, but
the scale dependence of hydraulic conductivity is not dependent on the specific
measurement method. In the present study, the scaling law of this parameter was
determined on a real confined aquifer, using measurements obtained, both in the
laboratory (flow cells) and the field (slug tests and aquifer tests). The
corresponding data were statistically analyzed. A scaling law was proposed for
both the laboratory and field scale, using the data obtained from flow cells, slug
tests, and aquifer tests. Afterward, the scaling law was estimated at just the field
scale, first using the slug tests and aquifer tests and then using only the aquifer
test data.
The scale dependence of the storativity was also investigated for all field
measurements and then using only the aquifer test data. In conclusion, for both
hydraulic conductivity and storativity, the trend to reach an upper bound increasing
the scale parameter was investigated in the scale ranges of 67 and 99 m,
respectively, examining only the data set relative to aquifer test measurements.
Estimation of Soil-Water Retention From Particle-Size Distribution: Fractal
Approaches
Ghanbarian-Alavijeh, Behzad; Hunt, Allen G.
Soil Science. 177(5):321-326, May 2012.
Soil-water retention curve (SWRC) is one of the most important properties of
porous media whose estimation is still under investigation by either physically
based approaches or empirically developed models. In this short communication,
the authors reviewed three well-known fractal approaches, that is, Kravchenko
and Zhang, the pore-solid fractal, and Hunt and Gee methods, which estimate
SWRC from particle-size distribution. The authors argue that the most reliable
method is to use Hunt and Gee’s approach to estimate SWRC, then modify the
estimated equilibrium water content by the Hunt and Skinner algorithm for
nonequilibrium conditions.
Temporal Variability of Bulk Density and Soil Water at Selected Field Sites
Logsdon, Sally D.
Soil Science. 177(5):327-331, May 2012.
Soil bulk density is not a fixed property but varies spatially because of soil
differences and temporally because of management and climate effects. The
purposes of this study were to determine the relation of bulk density and water
table depth with soil properties for wet and dry measurement dates and to
compare the correlation of soil properties with mass and volumetric water content.
Volumetric soil samples were collected at 15 or 16 field sites on 37 dates over 5
years. At the same time, water table depths were determined. The soil samples
were used to determine volumetric and mass water contents and bulk densities.
Other soil properties were used to develop orthogonal Principal Component 1
(PC1). The fractions of soil or landscape properties contributing to PC1 were as
follows: sand, 0.40; silt, −0.38; clay, −0.39; color index, −0.38; distance above
short-range low point, 0.35; distance above longer-range low point, 0.29; profile
curvature, 0.27; and plane curvature, 0.34. Principal Component 1 was positively
correlated with bulk density for 24 of 27 wet measurement dates, but only 4 of 10
dry dates. Volumetric soil-water content was negatively correlated with bulk
density for 9 of the 10 dry dates, but only 19 of the 27 wet dates. Mass water
content had slightly higher correlations with PC1 than did volumetric water
content, but both were significantly correlated for 36 of the 37 measurement dates.
Dividing measurement dates into “wet” and “dry” facilitated interpretation of bulk
density variation at the 15 or 16 sample locations.
Hydraulic Conductivity Increases in a Sodic Clay Soil in Response to Gypsum
Applications: Impacts of Bulk Density and Cation Exchange
Reading, Lucy P.; Baumgartl, Thomas; Bristow, Keith L.; Lockington, David A.
Soil Science. 177(3):165-171, March 2012.
Amelioration of sodic soils is commonly achieved by applying gypsum, which increases soil
hydraulic conductivity by altering soil chemistry. The magnitude of hydraulic conductivity
increases expected in response to gypsum applications depends on soil properties including
clay content, clay mineralogy, and bulk density.
The soil analyzed in this study was a kaolinite rich sodic clay soil from an irrigated area of
the Lower Burdekin coastal floodplain in tropical North Queensland, Australia. The impact of
gypsum amelioration was investigated by continuously leaching soil columns with a
saturated gypsum solution, until the hydraulic conductivity and leachate chemistry stabilized.
Extended leaching enabled the full impacts of electrolyte effects and cation exchange to be
determined.
For the columns packed to 1.4 g/cm3, exchangeable sodium concentrations were reduced
from 5.0 ± 0.5 mEq/100 g to 0.41 ± 0.06 mEq/100 g, exchangeable magnesium
concentrations were reduced from 13.9 ± 0.3 mEq/100 g to 4.3 ± 2.12 mEq/100 g, and
hydraulic conductivity increased to 0.15 ± 0.04 cm/d. For the columns packed to 1.3 g/cm3,
exchangeable sodium concentrations were reduced from 5.0 ± 0.5 mEq/100 g to 0.51 ± 0.03
mEq/100 g, exchangeable magnesium concentrations were reduced from 13.9 ± 0.3
mEq/100 g to 0.55 ± 0.36 mEq/100 g, and hydraulic conductivity increased to 0.96 ± 0.53
cm/d.
The results of this study highlight that both sodium and magnesium need to be taken into
account when determining the suitability of water quality for irrigation of sodic soils and that
soil bulk density plays a major role in controlling the extent of reclamation that can be
achieved using gypsum applications.
Emergent Behavior of Soil Fungal Dynamics: Influence of Soil Architecture and
Water Distribution
Falconer, Ruth E.; Houston, Alasdair N.; Otten, Wilfred; Baveye, Philippe C.
Soil Science. 177(2):111-119, February 2012.
Macroscopic measurements and observations in two-dimensional soil-thin sections indicate
that fungal hyphae invade preferentially the larger, air-filled pores in soils. This suggests that
the architecture of soils and the microscale distribution of water are likely to influence
significantly the dynamics of fungal growth. Unfortunately, techniques are lacking at present
to verify this hypothesis experimentally, and as a result, factors that control fungal growth in
soils remain poorly understood. Nevertheless, to design appropriate experiments later on, it
is useful to indirectly obtain estimates of the effects involved. Such estimates can be
obtained via simulation, based on detailed micron-scale X-ray computed tomography
information about the soil pore geometry. In this context, this article reports on a series of
simulations resulting from the combination of an individual-based fungal growth model,
describing in detail the physiological processes involved in fungal growth, and of a Lattice
Boltzmann model used to predict the distribution of air-liquid interfaces in soils. Three soil
samples with contrasting properties were used as test cases. Several quantitative
parameters, including Minkowski functionals, were used to characterize the geometry of
pores, air-water interfaces, and fungal hyphae. Simulation results show that the water
distribution in the soils is affected more by the pore size distribution than by the porosity of
the soils. The presence of water decreased the colonization efficiency of the fungi, as
evinced by a decline in the magnitude of all fungal biomass functional measures, in all three
samples. The architecture of the soils and water distribution had an effect on the general
morphology of the hyphal network, with a “looped” configuration in one soil, due to growing
around water droplets. These morphologic differences are satisfactorily discriminated by the
Minkowski functionals, applied to the fungal biomass.
Fractal Description of the Spatial and Temporal Variability of Soil Water Content
Across an Agricultural Field
Vidal-Vázquez, Eva; Paz-Ferreiro, Jorge; Vieira, Sidney; Topp, George; Miranda, José;
Paz González, Antonio
Soil Science. 177(2):131-138, February 2012.
There is an increasing interest in quantifying the space-time variation of soil properties. This
issue offers a unique set of problems that have been addressed using various methods.
Here, the spatial and temporal scaling behavior of topsoil water content at the field scale was
explored using the fractal approach. Results from fractal analysis were compared with those
from other methods describing either spatial variability or temporal trends and stability of soil
moisture. Time domain reflectometry probes were installed at the 0- to 20-cm depth in a clay
loam soil under natural pasture in Ottawa, Ontario, Canada. Soil water content was
measured 34 times at 164 points on a square grid with 10-m spacing. Mean soil water
content and coefficients of variation showed significant negative linear relationship for both
sampling dates (r2 = 0.783) and sampling points (r2 = 0.804). Both spatial and temporal data
sets were characterized by a self-affine fractal Brownian motion model that requires two
parameters, fractal dimension, D, and crossover length, l. For spatially sampled data sets at
different times, D ranged from 2.589 to 2.910 and l ranged from 0.95 to 6.97 m. For temporal
data sets measured on 10-m grid nodes, D was between 1.145 and 1.919 and l was from
0.069 to 9.40 days. Fractal analysis added information on the scale dependence of spatially
and temporally sampled data sets, which is not taken into account by classical statistics.
Also, interpretation of fractal parameters provided further insight when contrasted with
temporal stability analysis. Fractal dimension and crossover length of temporal series
showed spatial dependence, and ordinary kriging was used to map these two fractal
parameters.
Evaluation of Drip and Subsurface Drip Irrigation in a Uniform Loamy Soil
Rodríguez-Sinobas, Leonor; Gil, María; Sánchez, Raúl; Benitez, Javier
Soil Science. 177(2):147-152, February 2012.
Drip irrigation DI is considered one of the most efficient irrigation methods. Subsurface DI
(SDI) is also a localized irrigation method, but laterals are deployed underneath the soil
surface, leading to a higher potential efficiency.
Among other factors, water distribution in SDI is affected by soil hydraulic properties, initial
water content, emitter’s discharge, and irrigation frequency. However, complexity arising
from soil water and profile characteristics means that these are often not properly considered
in the design and management of these systems. In this article, irrigation uniformity in DI and
SDI laterals was determined by field evaluations in a loamy soil at different inlet head
pressures. Water application uniformity was very good for both irrigation methods, and
differences between them were negligible. Thus, both methods may be suitable for this soil
within the pressure range evaluated. The wetting pattern dimensions after infiltration for both
methods were simulated with Hydrus-2D under field conditions. Wetting bulb size for DI was
smaller than SDI; thus, it requires higher irrigation times to wet the same root zone. For the
loamy soil, an emitter depth greater than 10 cm is advisable to prevent soil surface wetting
for irrigation times higher than 30 min. Differences observed for 0.2- and 0.3-m depths were
negligible. Simulations for different scenarios are depicted in graphs that might aid at the
selection of proper design variables (emitter depth) and/or operation variables (inlet head
and irrigation time) in the studied soil. Similar graphs could also be developed for other soils.
Irrigation-Induced Changes in Phosphorus Fractions of Caribou Sandy Loam Soil
Under Different Potato Cropping Systems
He, Zhongqi; Zhang, Hailin; Zhang, Mingchu
Soil Science. 176(12):676-683, December 2011.
Sequential fractionation is a common method used in evaluating the impacts of soil
management practices on soil phosphorus (P) distribution. However, to our knowledge, this
method has not been used in investigating the effects of irrigation on the changes in soil P
fractions. In this work, we measured sequentially extracted P by deionized H2O, 0.5 M
sodium bicarbonate (pH 8.5), 0.1 M sodium hydroxide (NaOH), and 1 M hydrochloric acid
(HCl) in Caribou sandy loam soil samples from 10 potato fields under different 3-year crop
rotations both with and without irrigation. As inorganic fertilizer was applied to these fields,
irrigation and rotation management practices mainly affected the distribution of inorganic P
fractions, but had no significant changes of organic P fractions. The impact of crop rotation
was mainly reflected by H2O-extractable P. Irrigation had greater influence on stable or
recalcitrant P in NaOH, HCl, and residual fractions. Higher levels of NaOH-extractable
inorganic P were observed in soil from rainfed fields, whereas higher levels of HClextractable P were observed in soils under irrigated management. Our data indicate that
irrigation may eventually decrease P availability and runoff potential in these potato soils
over the long term because of the partial transfer of P in the sink from the active NaOH
fraction to more stable HCl and residual fractions. Whereas information and knowledge
derived from this study may shed some light on the transformation mechanism of soil P
fractions for sustainable agricultural production, more field data from short- and long-term
experiments are needed to confirm our observations.
Manure-Induced Soil-Water Repellency
Pagliari, Paulo H.; Flores-Mangual, Mario L.; Lowery, Birl; Weisenberger, Dwight G.;
Laboski, Carrie A. M.
Soil Science. 176(11):576-581, November 2011.
This laboratory study was conducted to evaluate the potential of nine manure samples from
dairy (n = 7), beef (n = 1), and swine (n = 1) to cause water repellency (WR) in six soils; in
addition, the duration of WR in two soils was assessed in an incubation study. Manures were
applied to supply 40 mg phosphorus (P) kg−1 to each soil. Sand content in the soils ranged
from 179 to 909 g kg−1. Water repellency was assessed with the water drop penetration
time (WDPT) and the degree of repellency with the soil wetted area (SWA) methods. The
potential for animal manure to induce WR measured with the WDPT method was dependent
on the manure type and soil series. Swine manure did not increase the WDPT of any soil;
beef manure increased WDPT in three of the six soils, whereas dairy manure had the
greatest effect on WDPT. Results of the SWA method were similar to those with the WDPT;
however, there were additional soil-water behavioral patterns identified by the SWA. For
example, dairy manure 5 increased WDPT of a soil from 1 to 9 sec, whereas the SWA
showed a decrease in the drop area from 120 mm2 in the control to 26 mm2 after manure
addition. Incubating manure-treated soils for 1 and 2 weeks decreased the induced WR in
the Antigo soil, but had little effect on the Rosholt. Field studies should be conducted to
assess these phenomena under natural climatic conditions.
Effects of soil moisture manipulations on fine root dynamics in a mature balsam
fir (Abies balsamea L. Mill.) forest
Jakub Olesinski, Michael B. Lavigne, Marek J. Krasowski1 and Michael Ryan
Tree Physiol (2011) 31 (3): 339-348.
We tested the hypothesis that moisture stress affects fine root dynamics during and after the
stress. To this end, we investigated the effects of soil moisture on annual and seasonal fine
root production and mortality over 4 years in a mature balsam fir (Abies balsamea L. Mill.)
stand using a minirhizotron and soil coring. Droughting and irrigating treatments were
imposed for 17 weeks during the third year of the study, and post-treatment recovery was
measured during the fourth year. Monthly fine root production was often reduced by low soil
water content (SWC) during July–September in the pre-treatment years and by imposed
drought. Irrigation resulted in higher summer fine root production than in pre-treatment
years. In the recovery year, increased fine root production was observed in the previously
droughted plots despite low SWC in August and September. Droughting decreased year-end
fine root biomass in the treatment year, but biomass returned to pre-treatment levels during
the recovery year. Droughting and irrigating did not affect foliage production during the
treatment and recovery years. Our results suggest that for balsam fir, establishment and
maintenance of a functional balance between foliage and fine root biomass, with respect to
moisture supply and demand, can depend on fine root dynamics occurring over more than
one growing season. In addition, our findings provided insights into tree growth responses to
interannual variation in moisture supply.